I have a fiberglass tub with an eight-inch crack that opens when I step into the tub. Can this be repaired without resurfacing the whole tub?

Fiberglass tubs and shower pans often crack because they have been reinforced with press board which deteriorates over time if it gets wet. This can be repaired by grinding out the crack, digging out the soggy particle board under the tub and replacing it with a special cement to add permanent reinforcement to the weak bottom. Then strips of fiberglass and resin are laid over the repaired area and a color matching fiberglass topcoat is applied which leaves an invisible, permanent repair.